While we, the maintainers of this book, strive to future-proof our texts, things can change and in the software industry, change happens often and quickly before writers have a chance to catch up. For example, this book was written when Firefox was still on Windows XP, an operating system Firefox no longer supports (and after August 2018, Mozilla will no longer issue security updates for it and Windows Vista). If you're still on Windows XP or Vista, you're recommended to upgrade to 7, 8, or 10. Alternatively, you can switch to a Linux distribution.